Now the two have taken the next step, creating a coloring book titled: "Coloring with Metro."

The book includes 30 drawings, Krajewski said.

The method behind it?

Krajewski draws an image, most of them of Metro's barn buddies, and then hands the pen to Metro who bobs his head up and down — creating lines overtop of Krajewski's original image. The result is an abstract piece, Krajewski said.

"He can hold a pen," Krajewski said. "I might as well put him to work."

It is available for sale on Amazon's website for around $6, but autographed copies by Metro sell for $25, Krajewski said. The proceeds of the personalized books are donated to New Vocations, a group that takes in about 400 retired racehorses each year and adopts them to willing families, said Dot Morgan, the nonprofit's executive director.

The pictures drawn by Metro and his owner resemble stained glass, said Krajewski's wife, Wendy.

"That's the beauty of it," she said. "It brings out a person's creativity; it's not your usual coloring book."